A transfer printing film for transfer printing patterns comprising any combination of logo, words, numbers, etc. on various kinds of articles generally includes a strip-shaped substrate film and an ink layer disposed on one side of the substrate film by means of gravure or screen printing to form the pattern. In the operation of applying pattern to the article, the transfer printing film is so placed that the pattern thereof is positioned in a predetermined printing area of a surface of the article, and the film is pressed to the article by a thermall pad under a certain pressure, whereby the heated ink layer is transfered from the substrate film to the article. Particularly, in case of printing patterns on golf balls, it is strongly desired that the transfered ink layer should not be removed easily.
Generally, the golf balls are, after the pattern was printed, subjected to urethane finish which is substantially carried out by spraying a two-component urethane paint. The clear urethane top coat covers the golf ball and the printed pattern to improve their appearance and to protect them from dirt, scratch, etc. But, when an adhesion between the urethane layer of the top coat and the ink layer of the printed pattern is weak, a hitting durability of the ink layer becomes low and the ink layer tends to be easily removed.
In order to enhance the adhesion between the two layers, Japanese Unexamined Patent Publication No.89214/95 discloses a transfer printing film for printing patterns on golf balls, whose ink layer contains as a vehicle a urethane resin having a predetermined hydroxyl value. Accordingly, when the two-component urethane paint is sprayed onto the golf ball, the hydroxyl-functioned urethane resin in the ink layer on the surface of the golf ball reacts with the isocyanate-functioned resins existing in one of the two components of the paint to form urethane bondings, and thus, the adhesion between the urethane finish layer and the ink layer becomes strong, a hitting durability is improved and the ink layer tends to be hardly removed.
On the other hand, the Patent Publication mentioned above teaches us that in the operation of applying pattern, the transfer printing film is pressed by a silicone pad heated up to 130.degree. C. to transfer the ink layer to the golf ball. It is known to the art that a lower transfer temperature is preferable by several reasons. One is, clearly, for reason of energy cost and the other for reason of heat damage of the article. When the article is a golf ball, for example, the ball and its dimples will be distorted under the higher transfer temperature. The higher transfer temperature may also cause a shrinkage of the substrate film which consists of a synthetic resin such as polypropylene, a glassine or a laminated paper composed of the two, and as a result, the shrinkage of the substrate film causes a crease or a distortion of the pattern transfered to the article. Moreover, it takes a longer time to heat the ink layer up to the higher temperature and a productivity will be lowered.
In this aspect, the transfer printing film according to the above-mentioned Patent Publication has a drawback that it is likely to need essentially a higher transfer temperature because the ink layer of which comprises as a main vehicle a urethane resin whose softening temperature is relatively high.
Consequently, it is an object of the present invention to provide a transfer printing film capable of printing patterns at a lower temperature, while realizing an enhancement of the adhesion between the patterns and the top coat.
On the other hand, as far as the transfer printing film for golf balls is concerned, it is specifically desired that the ink layer should have an enough flexibility to stretch on the spherical surface of the ball without a crack of the pattern, that the ink layer should be superior in adhesion to an ionomer resin coated on the ball surface, and that the pattern printed on the ball surface should not be blurred when spraying the urethane paint.
Accordingly, it is another object of the present invention to provide a transfer printing film for printing patterns on golf balls, which can meet the desires mentioned above.